Square dental anchor

ABSTRACT

A dental anchor is disclosed comprising an elongated body member for insertion into a channel in a tooth in order to anchor a superstructure to the tooth. The body member has at least one section with a substantially square cross-sectional configuration. The at least one section is provided with self tapping threads for threading into the channel. The threads have a root diameter approximately equal to the width of the square configuration, and a crest diameter less than the diagonal dimension of the square configuration. Preferably, the body member includes two similar sections joined together by a reduced thickness portion so that one section can be bent relative to the outer section when seated in the channel to provide an anchoring portion for the superstructure. Two dental anchors may be joined together by a reduced thickness frangible member, where the thickness of the reduced thickness portion of each dental anchor has a thickness greater than any thickness of the frangible member. Accordingly, the longitudinal side surfaces of the dental anchor are spaced from the walls of the channel when the anchor is seated in the channel to thereby relieve the stress on the tooth when threading the anchor into the channel. Additionally, it provides spaces therebetween, so that if cement is used, it can be disposed in these spaces.

BACKGROUND OF THE INVENTION

The present invention is a continuation-in-part application of Ser. No. 845,628 filed Oct. 26, 1977 by the applicant.

The present invention relates to dentistry in general, and more particularly to an improved dental anchor for building superstructures on broken or undermined dentition.

Anchoring a superstructure to the understructure of a tooth usually requires drilling a number of channels into the tooth or understructure. Depending upon the tooth involved, one or more anchoring rods are then secured in the channels and are allowed to protrude above the understructure with the exposed or protruding portions of the rods serving to anchor the superstructure. It should be noted, that in this type of dental operation, these rods are extremely small, for example, being on the order of 0.03" in diameter and approximately 0.20" in length.

The rods are retained in the channels by (1) cementation, by (2) being screwed into the channels, or by (3) friction lock where the rod is forced into a channel of smaller diameter. According to tensile tests performed on rods secured in dentin, self-threading rods have the greatest retention of the three types tested, where the friction lock is classified as intermediate, and the cemented rod is the least retentive.

It is noted, that prior art dental anchors are disclosed in my U.S. Pat. No. 3,434,209 showing a structure of a single dental anchor, and my U.S. Pat. No. 3,675,328 showing two dental anchors interconnected to one another which are readily severable from one another.

It is noted, that stresses are normally present when inserting the prior art dental anchors into the channels. Additionally, the construction of the prior art dental anchors require torque for insertion thereof into the channels provided in the tooth.

The aforementioned Ser. No. 845,628 provides one embodiment of the invention where the dental anchor has a substantially square cross-section to provide four longitudinal side surfaces joined by four longitudinal corner portions. Each of the corner portions are provided with threads for self-tapping the one section into the channel when the body member is rotated about its longitudinal axis.

Another prior art dental anchor and method for securing the anchor in a channel is described in U.S. Pat. No. 3,928,915. An improved cement is described in that patent which is used in conjunction with a dental pin having a square cross-section with the corners threaded in order to provide space between the pin and the channel to receive the improved cement. The pin has square corners and only the corners are threaded with a thread having a crest diameter greater than the diagonal dimension of the square configuration in order to insure that the corners remain square. This patent does not have self-tapping threads.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved dental anchor for building a superstructure on broken or undermined dentition.

Another object of the present invention is to provide an improved dental anchor which is fixedly secured in the understructure of a tooth.

A further object of the present invention is to provide an improved dental anchor which reduces the stresses normally present when inserting the prior art dental anchors into the channels provided in the understructure of a tooth, which also reduces the torque required during this insertion.

Still another object of the present invention is to provide a dental anchor in the form of sections with substantial square cross-sectional configurations, where self tapping threads are provided around the sections, with the thread having a root diameter approximately equal to the width dimension of the square configuration, and a crest diameter less than the diagonal dimension of the square configuration.

Yet another object of the present invention is to provide an improved dental anchor as set forth above, wherein the longitudinal side surfaces of the dental anchor are spaced from the walls of the channel when the anchor is seated therein to provide spaces therebetween, in order to relieve the stress to the tooth during insertion of the anchor into the channel.

Still a further object of the present invention is to provide an improved dental anchor having walls which are spaced from the walls of the channel when the anchor is seated therein so that, if desired, cement can be disposed in these channels to aid in securing the dental anchor in the channel.

These objects are achieved in accordance with a preferred embodiment of the present invention, wherein the dental anchor comprises an elongated body member having at least one section with a substantially square cross-sectional configuration, the at least one section being provided with self tapping threads for threading into the channel. The threads having a root diameter approximately equal to the width dimension of the square configuration and a crest diameter less than the diagonal dimension of the square configuration. The body member includes two similar sections joined together by a reduced thickness portion so that one section can be bent relative to the other section. Preferably, two dental anchors are joined together by a reduced thickness frangible member having a thickness less than the thickness of the above mentioned reduced thickness portion of each dental anchor. When the anchor is seated in the channel, the longitudinal side surfaces of the dental anchor are spaced from the walls of the channel to relieve the stress on the tooth when threading the anchor into the channel. Additionally, it provides spaces therebetween so that if cement is used it can be disposed in these spaces.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above additional objects and advantages in view, as will hereinafter appar, this invention comprises the devices, combinations and arrangements of the parts hereinafter described by way of example and illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 is a perspective view illustrating the dental anchor comprising the present invention;

FIG. 2 is a transverse sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view of a tooth or dentition with its surface excavated prior to building of a superstructure thereon, showing the first dental anchor inserted therein;

FIG. 4 is a cross-sectional view similar to FIG. 3 illustrating a bent dental anchor therein; and

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, FIG. 1 shows a dental anchor 10 of the present invention comprising two reinforcing or anchor rods 12, 14 interconnected to one another. However it is understood, that the present invention relates just as well to the construction of a single reinforcing or anchor rod and also to the construction of a dental anchor having more than two reinforcing or anchor rods interconnected to one another.

Each of the anchor rods 12, 14 includes first and second coaxial sections 16, 18 and 20, 22 which are joined together by intermediate reduced thickness portions 24 and 26. Additionally, section 18 of anchor rod 12 is joined to the section 20 of anchor rod 14 by a frangible reduced thickness portion 28 to define a one piece elongated dental anchor 10. The dimension of the reduced thickness portion 28 is selected such that it has a cross-sectional thickness less than that of the intermediate portions 24, 26 in order that the elongated body of the dental anchor 10 will fracture at this reduced thickness portion 28 after being inserted into a channel formed in the understructure of a tooth or dentition, in a manner as set forth in my above mentioned patents to which reference may be made.

As shown in FIGS. 1 and 2, each of the sections 16, 18, 20, 22 has a substantially square cross-section to provide each section with four longitudinal side surfaces joined by four longitudinal rounded corner portions, where the intermediate portions 24, 26 are cylindrical. Additionally, the sections 16, 18, 20, 22 are provided with self tapping screw threads 30. Preferably, at least one or all of the sections 16, 18, 20 and 22 has at least one end thereof terminating in a bevelled or chamfered end 32.

The anchor rods are formed from a square stock which has an initial width dimension and including corner square edges thereby providing a diagonal dimension. The threads are formed entirely around this square stock so that the entire circumference of the square is threaded. The thread has a root diameter 34 which is approximately equal to the width dimension of the square stock. In this manner, the thread will be substantially tangential at the side surfaces, as shown at 36. The crest diameter 37 is less than the diagonal dimension of the initial square stock. As a result, in forming the threads entirely around the square stock, the corners edges of the square stock will become rounded thereby eliminating the sharp square corner edges of the initial square stock. As a result, the initial square configuration will now have rounded edges with the flat side portions interconnecting the rounded corner portions.

The root diameter of the thread can preferably be slightly less than the width dimension of the square stock. In this manner, the thread will actually pass across the entire side surface 36 causing the thread to be formed even along this side surface and causing a slight groove 38 even at the tangential point of passing across the side surface. These grooves in the side surface will assist in holding the anchor to the cement, if cement is utilized in the space between the anchor and the walls of the channel to assist in securing the anchor into the channel. The grooves along the side surface will also assist in holding the anchor in the tooth even in the absence of the cement which will make the dental anchor of the present invention more secure in the tooth.

Referring to FIGS. 3, 4 and 5, the tooth 40 is prepared for building a super-structure thereon in the manner set forth in my above-mentioned patents, when a plurality of channels 42 having predetermined diameters are drilled therein. The dental anchors are now inserted into the channels 42, where the crest diameter of the anchor is greater than the diameter of each channel. The dental anchor can be rotated either by a manual tool or a power tool attached to the end section 22. The opposite end section 16 is thus threaded into the channel 42 by application of a slight downward pressure and simultaneous rotation of the dental anchor 10 as set forth above. Thus the threads 30 are self tapped into the tooth and form complementary threads in the walls of the channel to threadably engage the dental anchor.

It is noted, that the construction of this dental anchor is such that the threads at the corners will do most of the cutting into the tooth. This reduces the stresses normally present when inserting the prior art dental anchors into the channels. Additionally, the construction of the dental anchor of the present invention reduces the torque required for the insertion thereof into the channels provided in the tooth. Furthermore, it is noted that section 16 can also be provided with a chamfered end. Accordingly, either section 16 or 22 can be initially threaded into the channel, where both ends of the anchor can have the same configuration. By threading entirely around the square stock, most of the rounded corners will have spread sufficient to permit easy insertion into the channel and achieve self threading into the channel in a manner that will require less torque. At the same time, because there is sufficient threaded portions about the periphery of the square stock, there will be good securing of the anchor in the channels. At the same time, because a square stock is utilized and accordingly the thread depth will vary between the corner portions and the side portions, the stress on the tooth during the self tapping of the anchor in the tooth will be relieved.

Accordingly, it should be appreciated that the present configuration provides a unique compromise between stress relief and sufficient threads for self tapping into the tooth. With prior art configurations, there was either too much threads about the periphery of the anchor which provided too much stress on the tooth, or insufficient threads about the anchor whereby difficulty would be faced with self tapping. The present configuration provides quite a bit of threads about the periphery, especially at the corner portions but also along the sides, in order to provide adequate self tapping. At the same time, there will be spaces between the anchor sides and the channel wall to relieve such stresses.

In many cases the anchor will have sufficient adhesion in the tooth so that no additional cement is needed. However, should the use of cement be desired, the cement will be able to enter the space between the sides of the anchor and the channel wall. Furthermore, because of the grooves formed by the threads along the sides of the anchor, the anchor will be even more securely held by the cement.

Once the entire section 16 of the anchor 10 is seated in the channel 42 of the tooth 40, further rotation of the anchor will cause the frangible reduced portion 28 to break off, where the intermediate portion 24 and the rear section 18 will now protrude from the tooth as shown in the drawings. The anchor rod 14 is now ready to be threaded into a second channel 42 in the tooth in the same manner as above. The intermediate portion 24 will form a guide to aid in determining where to bend the anchor.

As shown in FIG. 4, the protruding section 18 is bent or inclined relative to the inserted section 16 to provide or anchoring portion for the superstructure, where the bending takes place along the intermediate portion 24 which has a reduced cross-section for this purpose. However, before the bending thereof, it may be desired to provide commercially available cement 44 or the like, which is well known in the art, into the channel 42. The cement 44 can be coated onto the section 16, can be inserted into the channel 42 before the insertion of the section 16, or can be applied after the insertion of the section 16, depending upon the requirements thereof.

It is noted, that the cement 44 functions to (1) seal the channel 42, (2) fixes the anchor section 16 in the channel 42, (3) prevents the anchor section 16 from turning or rotating after the cement has hardened, and (4) facilitates the bending of the dental rod by securing the dental end section 16 to the tooth 40. The grooves 38 formed by the threads 30 along the side sections of the anchor will aid in holding the tooth in the cement.

In one form of the invention, the threads are provided with a crest diameter of 0.030" and a root diameter of 0.027". Thus, the original square stock would have a width dimension of approximately 0.027" along each side. However, as indicated before, it might be beneficial to have the root diameter slightly less than the width dimension of the square stock in order to provide the grooves along the side sections of the anchor. The total length of the anchor, as shown in FIG. 1, is 0.38", with the reduced portion 28 being positioned midway therebetween at 0.19 inches from either end. The intermediate portions 24 and 26 are spaced midway between each half of the anchor. The diameter of the frangible reduced portion 28 was 0.018" and the reduced section of the intermediate portion for bending was 0.023".

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a preferred embodiment of the invention which is for purposes of illustration only and is not to be construed as a limitation of the invention. 

What is claimed is:
 1. A dental anchor for insertion into channels in a tooth, said dental anchor comprising:a first elongated body member, said first body member having at least one section with a substantially square cross-sectional configuration to provide four longitudinal substantially flat side surfaces joined by four longitudinal rounded corner portions, said one section being provided with thread means for self tapping said one section into a first channel when said body member is rotated about its longitudinal axis, said thread means having a root diameter approximately equal to the width dimension of the square configuration and a crest diameter less than the initial diagonal dimension of the square configuration, whereby said longitudinal side surfaces of said one section are spaced from walls of the first channel when said one section is seated in the first channel to reduce self tapping stresses; a second elongated body member along said longitudinal axis, said second body member having at least another section with a substantially square cross-sectional configuration to provide another four longitudinally flat side surfaces joined by another four longitudinal rounded corner portions, said another section being provided with second thread means for self tapping said another section into a second channel when said second body member is rotated about said longitudinal axis, said second thread means having a root dimension approximately equal to the width dimension of its square configuration and a crest diameter less than the initial diagonal dimension of its square configuration, whereby said another four longitudinal side surfaces of said another section are spaced from walls of the second channel when said another section is seated in the second channel to reduce self tapping stresses; a frangible reduced thickness member connecting said body members together; and each of said body members including a second section along said longitudinal axis and a reduced thickness portion disposed intermediate said sections of each of said body members to permit said second sections to be bent relative to said one section and said another section respectively after one section and said another section are seated in their channels respectively to provide anchoring portions for a superstructure, said reduced thickness portion of each said body members having a thickness greater than any thickness of said frangible reduced thickness member.
 2. A dental anchor according to claim 1, wherein said reduced thickness portions are each cylindrical.
 3. A dental anchor according to claim 1, wherein each said second section has a substantially square cross-sectional configuration to provide four additional substantially flat side surfaces joined by four additional rounded corner portions on each of said body members.
 4. A dental anchor according to claim 3, wherein each of said second sections respectively is provided with self tapping thread means having a root diameter approximately equal to the width dimension of its respective square configuration and a crest diameter less than the initial diagonal dimension of its respective square configuration. 